1. Field of the Invention
The present invention relates to an optical card.
2. Related Art Statement
Up to this time, an optical card disclosed in PCT/US82/00187 has been known. In this optical card, a metal record layer having high reflectivity is stuck to a substrate made of plastics etc., and data are recorded on the metal record layer as a black pit, i.e. a portion having low reflectivity by projecting a writing laser beam modulated by the data to be recorded thereon. When the recorded data are to be read out, a reading laser beam is projected on the metal record layer, and the data are read out by detecting a variation in reflectivity.
However, in the optical card mentioned above, since it is necessary to stick the metal record layer on the substrate, a skew might occur and thus flatness of the card surface cannot be maintained. Moreover, since the data for read only memory (ROM) is recorded by the laser beam, the cost for recording might be increased corresponding to the increase of the data to be recorded, and a recording error might occur due to an adhesion of dust etc. on the substrate. Further, in the known optical card, the data are recorded as the pit, constructed as a portion having low reflectivity by projecting the writing laser beam on the metal record layer having high reflectivity. Therefore, if a positional relation between a pit 1 and a receiving region 2 of a light receiving element on which light reflected by the pit 1 is projected is varied a little as shown in FIG. 7, the amount of reflected light is increased and thus the pit 1 cannot be normally detected. Therefore, the recorded data cannot be accurately read out.